1. Field of the Invention
The present invention relates to a process for the production of 1,2-butadiene from a polymerization-inhibitor-containing C.sub.4 hydrocarbon fraction by fractional distillation.
2. Description of the Prior Art
It is not possible to isolate 1,3-butadiene from a mixture of C.sub.4 hydrocarbons by simple distillation, since all components boil in a very narrow temperature range and, furthermore, some form azeotropic mixtures. For this reason, 1,3-butadiene is currently produced on an industrial scale by the extractive distillation principle. In this process, a solvent is fed in an extraction column to a gaseous C.sub.4 hydrocarbon mixture from naphtha or middle distillate pyrolysis. This solvent primarily dissolves 1,3-butadiene, which is selectively extracted as a result. The 1,3-butadiene-containing solvent thus remains in the bottom of the column, while the residual C.sub.4 fraction distils off overhead. As solvent, use is made, for example, of sulfolane, N-methylpyrrolidone (NMP), dimethylformamide, acetonitrile or dimethylacetamide. To avoid the unwanted thermal polymerization of 1,3-butadiene in the course of the extractive distillation, polymerization inhibitors are added both to the feed fraction of the extractive distillation and to the bottom product of solvent and 1,3-butadiene. These polymerization inhibitors are, for example, 4-tert-butylcatechol (TBC). In the course of the subsequent separation operations for purifying the 1,3-butadiene, distillation residues of C.sub.4 and C.sub.5 hydrocarbons which comprise these polymerization inhibitors, sometimes in considerable amounts, therefore arise. It is generally customary to destroy distillation residues or bottom products of this type from the purification of 1,3-butadiene. This is generally performed by combustion via a flare or by other thermal utilization. In this procedure, valuable hydrocarbons which are suitable for material utilization are lost.
DD 246 009discloses a process for working up such distillation residues which arise in the extractive distillation of C.sub.4 hydrocarbon fractions for the production of 1,3-butadiene and comprise dissolved polymerization inhibitors. In this process, the inhibitor/C.sub.4 hydrocarbon mixture is firstly introduced into a preferably aromatics-containing hydrocarbon mixture whose initial boiling point is 50-200K higher than the boiling point of the C.sub.4 hydrocarbon fraction and is then thermally treated. In this case the temperature is set so that the C.sub.4 hydrocarbon fraction evaporates and can thus be completely removed. In the bottom of the column accordingly remains a mixture of the higher-boiling, preferably aromatic hydrocarbons, in particular C.sub.8 - and C.sub.9 aromatics, the high boilers, the contaminants and the polymerization inhibitor. This process thus makes it possible to separate off the C.sub.4 hydrocarbon fraction as such from the contaminants and high boilers and also, in particular, from the inhibitor. The total C.sub.4 hydrocarbon fraction is passed to material or caloric utilization; further fractionation into the various components is not described.
However, it is desirable to produce the individual compounds from C.sub.4 hydrocarbon fractions of this type. Especially the C.sub.4 component 1,2-butadiene is increasingly gaining importance and is used as polymerization regulator in the preparation of synthetic rubber from 1,3-butadiene. 1,2-butadiene is also a synthesis building block of interest for the production of perfumes. Thus, the reaction of 1,2-butadiene with acetaldehyde gives cis-3-hexenol, i.e. leaf alcohol.
The object of the present invention was thus to provide a process which enables the production of pure 1,2-butadiene in a simple manner from C.sub.4 hydrocarbon fractions.